Spark-plug



A. SCHMIDT.

SPARK PLUG.4

Arlon FILED Nov. 22, 19

APPLIC l?. 1,358,1 1 6. Patented Nov. 9,1920.

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, l {lffozucs UNITED STATES PATENT OFFICE.

ALBERT SCHMIDT, OF FLINT, MICHIGAN, ASSIGNOR TO CHAMPION IGNITION A COMPANY, OF FLINT, MICHIGAN, A CORPORATION OF MICHIGAN.

SPARK-PLUG'.

Application filed November 22, 1917.

To all whom t may concern.'

Be it known that I, ALBERT SCHMIDT, a citizen of the Republic of France, residing at Flint, in the county of Genesee and State of Michigan, have'invented certain new and useful Improvements in Spark-Plugs, of which the following is a specification,` reference being had therein to the accompanying drawings.

The invention relates to spark-plugs and comprises the novel construction as hereinafter set forth.

In the drawings:

Figure 1 is a longitudinal section through the plug;

Figs. 2 and 3 are `cross-sections on lines 2 2 and 3-8 of Fig. f

A is the casing of a plug having the usual threaded nipple B for engagement with the engine casing. C is the insulator and D is the electrode passing therethrough. The insulator C is provided with an inner end portion E, which is arranged within the p01'- tion B of the casing, and beyond this portion the insulator is enlarged to form a shoulder Fior fitting against a corresponding shouldei' G on the casing. H is a gasket between the shoulders F and G for forming the gas seal, and I is an opposed shoulder on the outer portion of the insulator, which is engaged by a turned-in Hangs J on the casing for holding the shoulders G and H in sealing relation to each other. f I

As usually constructed plugs of this type have the portion of the insulator extending between the shoulders \F and I of uniform diameter and fitting with a slight clearance within the outer casing.- As the insulator is formed of material which yis low in thermal conductivity it is desirable to limit the size and mass of the sante, particularly in the portion which is eirposed to t eA flame and between the end of' the electrode and the point of bearing F on the casing. On the other hand, if the diameter of the insulator is too -small the mechanical-stress to which it is subjected' in closing in the flange I (this operation being performed when the metal of the c'ase'sV heated) and the subsequent stress exerted by this -ange wouldV endanger cracking of the structure. I have Speciication of Letters Patent.

Patented Nov. 9, 1920.

Serial No. 203,298.

thereforeconstructed the insulator and casing with a portion of the former extending to the shoulder bearing F of restricted diameter, and above this bearing have enlarged the diameter of the insulator and correspondingly enlarged the casing to recelve the same. As a result the annular bearing I over which the flange J is turned is sufliciently enlarged to more safely stand 'the mechanical stresses, while at the sanne time the mass of' material which 1s exposed to the heat is not enlarged. I have found that only a slight increase in the diameter of the `upper portion of the insulator will greatly increase its mechanical strength and will correspondingly decrease the percentage of breakage.

' What I claim as my invention is: y a l. In a spark-plug, an insulator having an inner portion which is exposed to the heat, a portion beyond the saine of larger diame ter forming a shoulder and a portion beyond the shouldered portiony of still larger diameter having an opposed shoulder formed thereon, all of said portions being integral in combination with a casing having a portion substantially Fitting the inner shouldered portion of said insulator and providing a seat therefor, a portion enlarged in internal diameter for receiving the enlarged portion of said insulator and an inturned flange on said enlarged portion for engaging the opposed shoulder ,on the enlarged portion of the insulator.

2. In a spark-plug, an insulator having an inner portion exposedto the heat, a cylindrical portion beyond the same enlarged in diameter'with a conical seat portion inbearing against the shoulder on this latter rateale tioned portion providing a substantial structure for projecting beyond the casing and also an opposed shoulder Jfor a clamping bearing on said casing, there being no other points of bearing for said insulator upon v said casing.

ln testimony whereof l ax my signature.

ALBERT SCHMlDT. 

